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<br />43 <br /> <br />S_tep. e _-_C()~u_t..e Flood Da nla'les_J 01'_ jh~__Base Line Cond it ion <br /> <br /> <br />A. Establish Base Line Conditions <br /> <br /> <br />The "Base Line' condition defines what is likely to happen if no <br /> <br /> <br />UDFC alternative plan is implemented. It is the datum against which <br /> <br /> <br />the effectiveness of altel^native flood control schemes will be measured. <br /> <br /> <br />The effectiveness of each alternative is measured by 110Vl lilli\.h it reduces <br /> <br /> <br />the flood damages from the "Base Line" case considered. <br /> <br /> <br />Since an effective flood plain regulation is in effect, the "Base- <br /> <br /> <br />line" condition will assume that future flood plain development will be <br /> <br /> <br />"contro 11 ed. " <br /> <br /> <br />B. Assemble Data Needed to Compute Damages <br /> <br /> <br />For this case, benefits are calculated for direct and indirect <br /> <br /> <br />flood damage reduction. To establ iSh them, engineerin(j data are ,^e- <br /> <br /> <br />quired from the hydrologic and hydraulic analyses WhlCh include: <br /> <br /> <br />1. Tributary basin flood hydrographs for the required <br /> <br /> <br />recurrence intervals for future basin rlevelopment con- <br /> <br /> <br />ditions. In this case, fully developed future conditions <br /> <br /> <br />are used for the analysis. <br /> <br /> <br />2. Delineation of the corresponding flood plains on adequate <br /> <br /> <br />topographic mapping. <br /> <br /> <br />3. Estimates of flood depths and velocities. <br /> <br /> <br />Other data necessary for the damage analysis are: <br /> <br /> <br />1. Structural data - Residential and Commercial <br /> <br /> <br />For Little Dry Creek structural data were obtained <br /> <br /> <br />from computer printouts of the County Assessor's records <br /> <br /> <br />of properties located in and around the flood plain. The <br /> <br /> <br />data obtained for each property were: <br />